The present invention relates to a method for displaying half tone for a display panel such as a plasma display panel (PDP) and a liquid crystal display (LCD) of a matrix display type. In the method, a unit display period (one frame or one field) is divided into a plurality of sub-frames corresponding to a display tone. The number of display pulses (discharge sustaining pulses) of each sub-frame is weighted corresponding to each bit.
Recently, as a display device becomes large in size, thickness of the display device is desired to be thin. Therefore, various types of display devices of thin thickness are provided. As one of the display devices, an ACPDP is known.
A conventional ACPDP comprises a plurality of data electrodes, and a plurality of row electrodes formed in pairs and disposed to intersect the data electrodes. A pair of row electrodes form one row (one scanning line) of an image. The data electrodes and the row electrodes are covered by dielectric layers respectively, at a discharge space. At the intersection of each of the data electrodes and each pair of row electrodes, a discharge cell (pixel) is formed.
As a method for displaying an image on the PDP by controlling a tone of the image, each frame (field) of a video signal is divided into N pieces of sub-frames (sub-fields), and each sub-frame (sub-field) emits the light for a time length corresponding to a weight applied to each bit of n-bit pixel data (sub-frame method).
In the method, if a pixel data for each pixel has 6 bits, each frame is divided into six sub-frames, SF1, SF2, . . . SF6. The sub-frames SF1 to SF6 emit the light by sustaining discharge at 1 time, 2 times, 4 times, 8 times, 16 times and 32 times, respectively, in order. Thus, the tone of 64 steps can be obtained by combining the six sub-frames.
There are two cases in the PDP that, a video signal (interlace video signal) produced by the interlace scanning as used in the NTSC system is displayed, and that a video signal (non-interlace video signal) produced by the non-interlace scanning as used in the personal computer is displayed.
In the NTSC system, the interlace video signal is normally used for displaying a moving picture. On the other hand, in the personal computer, the non-interlace video signal is used for displaying the computer picture image which consists of a still picture without a moving picture or a moving picture without a still picture.
In order to display both of the still picture and the moving picture by the half tone display method, since the display order of the sub-frames is constant fixed), false contours are recognized irrespective of he still picture or the moving picture.
The false contour of the still picture is a flicker caused by brightness fluctuation with time of the same pixel (discharge cell). In the false contour of the moving picture, when an image is moved in plane on the PDP, false contours of bright stripes or dark stripes are recognized as if the tone of the image is lost near the area where the image crosses the border at the tone level of the n power of 2. Therefore, the quality of display is extremely deteriorated.